PHYSIOLOGICAL CHEMISTRY 437 



check, it may be made by diluting 125 c.c. of urine with 75 c.c. water, adding 

 30 c.c. dilute hydrochloric acid (1:4) and precipitating the inorganic sulphates 

 with 20 c.c. of 5 per cent, solution of barium chloride, as above described. After 

 standing for one hour the mixture is filtered through a dry filter and 125 c.c. of 

 the clear filtrate, corresponding to 62'5 c.c. original urine, boiled for not less than 

 30 minutes, whereby a precipitate of sulphate forms on account of the decomposi- 

 tion of the ethereal sulphates. After allowing the solution to cool, this precipitate 

 is collected on a Gooch crucible, washed, ignited, and weighed. 



EXPERIMENT VIII. Total Sulphur. 25 c.c. urine (or 50 c.c. if very dilute) 

 is mixed in a large nickel crucible (of 200 to 250 c.c. capacity) with 3 grams of 

 sodium peroxide. The crucible is then carefully heated until its contents solidify 

 (about 15 minutes), after which it is cooled, the fused mass moistened with 1-2 c.c. 

 of water about 7 grms. of sodium peroxide sprinkled over it, and again heated to 

 cause its contents to become completely fused; the mass is kept fused for ten 

 minutes, then allowed to partially cool, 100 c.c. water added and the contents 

 boiled for half an hour. This dissolves the alkali and decomposes all the sodium 

 peroxide. The contents of the crucible are transferred to an Erlenmeyer flask 

 (400 450 c.c. capacity) and the crucible washed into the flask with hot water, 

 the volume of the resulting solution made up to about 250 c.c., and then brought 

 almost to the boil ; concentrated hydrochloric acid is now slowly added until the 

 nickelic oxide just dissolves (about 18 c.c.) and the mixture is boiled until it 

 becomes clear. (If it does not become clear by this treatment, it must be cooled 

 and filtered.) 5 c.c. of dilute alcohol (1 : 4 ) is then added and the boiling 

 continued for a few minutes, so as to remove traces of chlorine. 



The solution is now ready for precipitation of the sulphates, into which, by the 

 above procedure, all the sulphur has been converted. To do this 10 c.c. of 10 

 per cent, solution of barium chloride is added drop by drop, as above described, 

 and the mixture allowed to stand for two days, 1 after which the precipitate is 

 collected and weighed as above described. 



EXPERIMENT IX. Neutral Sulphur. This is obtained by subtracting the 

 total sulphates (No. 2) from the total sulphur. 



It will be seen that at least three separate estimations must be carried through 

 to obtain all the desired data (1) inorganic sulphates, (2) total sulphates, and (3) 

 total sulphur. The ethereal sulphates and the neutral sulphur can be calculated 

 by difference. 



These values can be calculated as S or SO 3 according to the following ratios : 



BaS0 4 : S = 1 : 0'1374 ; BaS0 4 : S0 3 = 1 : 0'3429. 



Metabolism. One of the results of Folin's investigations on 

 metabolism has been to show the significance of determinations of 

 sulphates in the urine. The total sulphur in the urine is, like the 

 nitrogen, distributed among several substances, which are divided into 

 three groups the inorganic sulphates, the ethereal sulphates, and the 

 neutral sulphur compounds. The inorganic sulphates are mainly those 

 of sodium; the ethereal sulphates are compounds of phenol, cresol 

 skatoxyl, and indoxyl, with sulphuric acid and potassium (see p. 435), 

 and the neutral sulphur compounds are organic compounds in which 



1 It takes this length of time to ensure complete precipitation. 



